Vibration dampener for motor vehicle drive shaft

ABSTRACT

Vibrations are dampened in a normally straight drive shaft for automobiles through the use of a plurality of cylindrical vibration dampening masses disposed at locations on the shaft corresponding to the nodal points of the smallest harmonic of the natural bending frequency of the shaft occurring at a rotational speed greater than the maximum normal operating speed of the shaft.

United States Patent Doehring et al.

[4 1 Aug. 1,1972

VIBRATION DAMPENER FOR MOTOR VEHICLE DRIVE SHAFT Inventors: Ekkehard Doehring; Peter Kirschner, both of Wolfsburg, Germany Assignee: Volkswagenwerk Akt., Wolfsburg,

Germany Filed: May 10, 1971 Appl. No.: 141,503

Related U.S. Application Data Continuation of Ser. No. 837,151, June 27, 1969, abandoned.

' Foreign Application Priority Data July 2, 1968 Germany ..P 17 55 860.0

Us. 01. ..74/574, 64/1 v, 188/1 B Int. Cl. ..Fl6f 15/02 Field of Search ..74/574; 64/1 V, 13, 15, 21; 308/26, 184 R; 188/1 B [56] References Cited UNITED STATES PATENTS 3,037,573 6/1962 Larsen ..308/184 R x 2,857,974 10/1958 Heller ..308/184 R x 1,958,982 5/1934 Wintercorn ..'..64/l V X 2,092,291 9/1937 Olsen ..308/184 R 3,292,389 12/1966 Adlotf et a1 ..64/1 v Primary Examiner-William F. ODea Assistant Examiner-F. D. Shoemaker Att0rney-Watson, Cole, Grindle & Watson 5 7] ABSTRACT Vibrations are dampened in a normally straight drive shaft for automobiles through the use of a plurality of cylindrical vibration dampening masses disposed at iocations onthe shaft corresponding to the nodal points of the smallest harmonic of the natural bending frequency of the shaft occurring at a rotational speed greater than the maximum normal operating speed of the shaft.

10 Claims, 5 Drawing Figures PATENTEDMJS H972 3.6800407 SHEET 1 or a a; n h 7 Hi I H w {F fi 1L t WFTIVE A '7 Z9 SUBTRACTIVE I GEAR BOX DIFFERENTIAL GEAR Bog 40 X 4 jaw PRICE oouNTER 5, 5/ if) 54 /J PRICE INcREMENT f SUMMING 55 UNIT DIFFERENTIAL i H 50! a;

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INVENTORZ VIBRATION DAMPENER FOR MOTOR VEHICLE DRIVE SHAFT CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation of copending application Ser. No. 837,151, filed June 27, 1969, now abandoned. Applicants claim priority from corresponding German patent application Ser. No. P 17 55 860.0, filed July 2, 1968.

BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to a vibration dampening system for a straight automotive drive shaft. In particular, the dampener system is utilized with a straight drive shaft which comprises a thin metal rod extending from a front mounted engine to the rear driven wheels of the vehicle.

2. Description of the Prior Art A well known prior art method for preventing vibration in drive shafts is to construct them of such rigid materials that the natural first mode bending frequency of the shaft occurs at a rotational speed which is greater than the normal maximum operating speed of rotation thereof and the shaft therefore remains subcritical. Such rigid shafts are bulky and expensive. Thus, it is desirable to utilize drive shafts comprising thin metal rods having a natural bending frequency which occurs at a rotational speed below the normal operating range of the shaft. Such a shaft construction is desirable because the shaft has a small moment of inertia and torsional softness thereby facilitating good dampening of coupling shocks and the like. However, vibrations of higher order harmonics of the natural bending frequency, for example the second and third harmonics, cause considerable difficulties in this type structure and therefore such shafts have in the past been generally encased in a pipe and guided therein by a plurality of intermediate hearings in order to achieve subcritical operation. Necessarily, such guide pipes must be rigid to remain subcritical and prevent vibrations and resultant noise.

Another prior art construction featuring a thin metal shaft involves bending of the shaft and rotation thereof in a bent state. The first mode bending frequency of a shaft is increased as a result of these measures. However, it is not possible, in the case of drive shafts of a practical constructional length for motor vehicles, to raise the first mode bending frequency of the shaft to a value such that it occurs at a rotational speed above the normal operational speed of the shaft. Therefore, the first mode bending frequency will occur within the operational range. Further, harmonics of the first mode bending frequency will be only slightly influenced by the flexure so that harmonics of low order, such as the second harmonic, will likewise generally occur within the working range. Since operation at the first mode bending frequency and its harmonics will lead to circularly polarized vibrations caused by slight unavoidable stimulations, this solution is not practical.

SUMMARY OF THE INVENTION It is, therefore, an object of the invention to provide structure to dampen, by simple measures, vibrations in a shaft caused by the fact that harmonics of the first mode natural bending frequency of the shaft occur at a rotational speed within the normal working range of the shaft.

According to the invention, vibration dampeners are connected with the shaft for dampening harmonics which occur at a rotational speed in the working range. A vibration dampener constructed in accordance with the invention comprises structure capable of vibrating consisting of a spring-mass system tuned to harmonics of the first mode natural bending frequency of the shaft.

The invention is utilized advantageously in connection with a motor vehicle having a front mounted engine and rear mounted transmission and differential gearing. The normal rotational speed range of the drive shaft therefore corresponds to the rotational speed range of the engine and not to the rotational speed range of the wheels. Generally, only the second and third harmonics of the first mode natural bending frequency of the drive shaft will occur at a rotational speed within the working range of the shaft. Preferably, therefore, three vibration dampeners will be placed at locations on the shaft corresponding to the three nodal points of fourth harmonic vibrations.

The vibration dampeners should have no sharply defined natural vibrational frequency of their own, but they should be capable of acting over a more or less broad frequency range, a situation which can be achieved by utilizing dampeners having several differing frequencies (or spring constants). The differing frequencies of a dampener can also be assigned to different harmonics that are to be dampened.

The dampeners may preferably be isolated torsionally from the shaft by interposition of a bearing, preferably an antifriction bearing such as a roller bearing. The directions or planes of vibrations of the dampeners may be varied, by a relative twisting of the dampeners of the same structure.

The optimum disposition of the dampeners must ultimately be determined by trial and error and for that reason, only the base principle of a vibration dampener system constructed in accordance with the present invention will be explained in the following description of a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view showing a drive shaft of the type contemplated by the present invention along with a representation of its forms of vibrations;

FIG. 2 is a perspective view of the shaft;

FIG. 3 is a cross-sectional elevational view of a drive shaft and a vibration dampener system which embodies the invention;

FIG. 4 is a diagrammatic view of a shaft according to the invention with pipelike dampeners connected thereto; and

FIG. 5 is an enlarged sectional view of a portion of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The vibrations of a thin freely revolving normally straight shaft 1 show the vibration image represented in FIG. 1, in which the number of antinodes or loops of 7. Structure for dampening vibrations in a drive shaft for motor vehicles comprising an elongated, normally straight rod having a first mode natural bending frequency which occurs at a rotational speed less than the normal minimum rotational speed of the shaft, said structure comprising a plurality of dampener devices connected to said shaft, each of said devices including a cylindrical mass surrounding the shaft, said masses being disposed for dampening harmonics of said first mode natural bending frequency, there being an antifriction device provided between each mass and the shaft whereby the latter is rotatable relatively to the masses, said masses being supported against rotation by resilient flexible means attached between the masses and the vehicle itself, said resilient flexible means comprising a rubber band, there being a hook attached to the mass and a stationary hook on the vehicle, said band being looped around the hooks.

8. Structure as set forth in claim 7 wherein said masses are disposed at locations along the shaft cor responding to the nodes of the smallest harmonic of said natural frequency which occurs at rotational speed greater than the maximum rotational speed of the shaft.

9. Structure as set forth in claim 8 wherein said masses are disposed at locations corresponding to the three nodes of the fourth harmonic of said natural frequency.

10. Structure as set forth in claim 7, wherein the directions of vibration of the dampeners are relatively offset circumferentially of the shaft.

. UNITED STATES PATENT OFFICE CERTIFICATE 0F COECTIN Patent No. 3,680,407 Dated August 1, 1972 Inventor(s) Doehring Ekkehard, .et. a1.

It is certified that error appears in the above-identified patent .and that said Letters Patent are hereby corrected as shown below:

Cancel the 3 sheets of drawing and substitute the attached sheets in their place. Cancel the figure illustrated on the front page format and substitute Fig. l of the attached drawings.

Signed and sealed this 26th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM uscoMM-Dc 60376-P6D lLS. GOVERNMENT PRINTING OFFICE 1 19.9 0"365'334,

PatentNo. 3,680,407 Dated August 1, 1972 Inventors Doehring Ekkehard, et. a1. --2-- SHEET 1 OF 2 FIG? INVENTORS E D01: l-L7zg BYP Kai-6021277 e}- mwz/Lgfv 14% Patent No. 3,680,407 Dated August 1,1972 Inventors Doehring Ekkehard, et. a1. --3--- sum 2 or 2 INVENTORS E. DIDZIFLWQ I' mhsclnvk 

1. Structure for dampening vibrations in a drive shaft for motor vehicles comprising an elongated, normally straight rod having a first mode natural bending frequency which occurs at a rotational speed less than the normal minimum rotational speed of the shaft, said structure comprising a plurality of dampener devices connected to said shaft, each of said devices including a cylinDrical mass surrounding the shaft, said masses being disposed for dampening harmonics of said first mode natural bending frequency, adjacent masses being interconnected by cylindrical rubber springs extending therebetween, there being provided antifriction devices mounting the springs on the shaft for rotation of the latter relative to the springs.
 2. Structure as set forth in claim 1 wherein said masses are disposed at locations along the shaft corresponding to the nodes of the smallest harmonic of said natural frequency which occurs at rotational speed greater than the maximum rotational speed of the shaft.
 3. Structure as set forth in claim 2 wherein said masses are disposed at locations corresponding to the three nodes of the fourth harmonic of said natural frequency.
 4. Structure as set forth in claim 1 wherein the directions of vibration of the dampeners are relatively offset circumferentially of the shaft.
 5. Structure as set forth in claim 1 wherein the masses disposed at the ends of the shaft are secured to the vehicle to prevent rotation thereof.
 6. Structure for dampening vibrations in a drive shaft for motor vehicles comprising an elongated, normally straight rod having a first mode natural bending frequency which occurs at a rotational speed less than the normal minimum rotational speed of the shaft, said structure comprising a plurality of dampener devices connected to said shaft, each of said devices including a cylindrical mass surrounding the shaft, said masses being disposed for dampening harmonics of said first mode natural bending frequency, there being an antifriction device provided between each mass and the shaft whereby the latter is rotatable relatively to the masses, said masses being supported against rotation by resilient flexible means attached between the masses and the vehicle itself, said resilient flexible means comprising a rubber cylinder extending axially of the shaft in surrounding relationship thereto.
 7. Structure for dampening vibrations in a drive shaft for motor vehicles comprising an elongated, normally straight rod having a first mode natural bending frequency which occurs at a rotational speed less than the normal minimum rotational speed of the shaft, said structure comprising a plurality of dampener devices connected to said shaft, each of said devices including a cylindrical mass surrounding the shaft, said masses being disposed for dampening harmonics of said first mode natural bending frequency, there being an antifriction device provided between each mass and the shaft whereby the latter is rotatable relatively to the masses, said masses being supported against rotation by resilient flexible means attached between the masses and the vehicle itself, said resilient flexible means comprising a rubber band, there being a hook attached to the mass and a stationary hook on the vehicle, said band being looped around the hooks.
 8. Structure as set forth in claim 7 wherein said masses are disposed at locations along the shaft corresponding to the nodes of the smallest harmonic of said natural frequency which occurs at rotational speed greater than the maximum rotational speed of the shaft.
 9. Structure as set forth in claim 8 wherein said masses are disposed at locations corresponding to the three nodes of the fourth harmonic of said natural frequency.
 10. Structure as set forth in claim 7, wherein the directions of vibration of the dampeners are relatively offset circumferentially of the shaft. 